Ultrasonic probes provide a convenient and accurate way of gathering information about various structures of interest within a body being analyzed. In general, the various structures of interest have acoustic impedances that are different than an acoustic impedance of a medium of the body surrounding the structures. In operation, such ultrasonic probes generate a signal of acoustic waves that is then acoustically coupled from the probe into the medium of the body so that the acoustic signal is transmitted into the body. As the acoustic signal propagates through the body, part of the signal is reflected by the various structures within the body and then received by the ultrasonic probe. By analyzing a relative temporal delay and intensity of the reflected acoustic waves received by the probe, a spaced relation of the various structures within the body and qualities related to the acoustic impedance of the structures can be extrapolated from the reflected signal.
For example, medical ultrasonic probes provide a convenient and accurate way for a physician to collect imaging data of various anatomical parts, such as heart tissue or fetal tissue structures within a body of a patient. In general, the heart or fetal tissues of interest have acoustic impedances that are different than an acoustic impedance of bodily fluids surrounding the tissue structures. In operation, such a medical probe generates a signal of acoustic waves that is acoustically coupled from the probe into the medium of the patient's body, so that the signal is transmitted into the patient's body.
In a catheter-type probe, capable of imaging inside of a blood vessel or artery, acoustic coupling is achieved by inserting the probe into the patient's body and through the blood vessel or artery. For example the probe includes a probe housing that contains an ultrasonic transducer. The transducer generates a beam of acoustic signals, which are transmitted through the probe housing. The ultrasonic beam scans the interior of the blood vessel.
In other cases, such as vaginal or trans-esophageal probes, acoustic coupling is achieved by inserting the probe into a bodily orifice. Alternatively, with abdominal probes, less invasive means are used to achieve acoustic coupling, such as pressing the front portion of the probe into contact with a surface of the abdomen of the patient.
Typically, such probes are mechanically scanned by moving an ultrasonic transducer within the probe. For example, a front portion of such a probe includes a hemispherical housing that contains a moveable ultrasonic transducer. The housing is pressed into contact with a patient's tissue during operation of the probe. A beam of acoustic signals generated by the transducer is transmitted through the housing so as to analyze the patient's tissue. A motor coupled to the transducer causes the transducer to mechanically scan back and forth, so as to sweep the beam of acoustic signals through the patient's tissue.
In general, as the acoustic signal propagates through the patient's body, portions of the signal are weakly reflected by the various tissue structures within the body and received by the ultrasonic medical probe. As the weakly reflected acoustic waves propagate through the probe, they are electrically sensed by electrodes coupled thereto. By analyzing a relative temporal delay and intensity of the weakly reflected waves received by the medical probe, imaging system components that are electrically coupled to the electrodes extrapolate an image from the weakly reflected waves to illustrate spaced relation of the various tissue structures within the patient's body and qualities related to the acoustic impedance of the tissue structures. The physician views the extrapolated image on a display device coupled to the imaging system.
Since the acoustic signal is only weakly reflected by the tissue structures of interest, it is important to try to provide efficient acoustic coupling between the probe and the medium of the patient's body. Such efficient acoustic coupling would insure that strength of the acoustic signal generated by the probe is not excessively diminished as the signal is transmitted from the probe into the medium of the body. Additionally, such efficient acoustic coupling would insure that strength of the weakly reflected signal is not excessively diminished as the reflected signal is received by the probe from the medium of the body.
An impediment to efficient acoustic coupling is an acoustic impedance mis-match between an acoustic impedance of a material of the probe housing and an acoustic impedance of the medium under examination by the probe. For example, one material for the probe housing is acrylic plastic, which has an acoustic impedance of approximately 3.26*10.sup.6 kilograms/meter.sup.2 second, kg/m.sup.2 s. The acoustic impedance of acrylic plastic is mis-matched with an acoustic impedance of human tissue, which has a value of approximately 1.5*10.sup.6 kg/m.sup.2 s.
What is needed is an ultrasonic probe that provides enhanced operational performance, while further providing efficient acoustic coupling to the desired medium under examination by the probe.